Apparatus for production of polyamide moldings

ABSTRACT

An apparatus for the production of moldings by activated anionic polymerization of lactams in which a lactam melt containing a catalyst and a lactam melt containing an activator are separately preheated to polymerization temperature in two melt reservoirs and supplied to a control unit including a pair of valves and a vertically oriented mixing chamber, mixed therein, and forced upwardly into the mold to be filled wherein valve seats for the respective valves are in the wall of said mixing chamber.

United States Patent [191 Sinn et a1.

[ Aug. 14, 1973 Assignee:

APPARATUS FOR PRODUCTION OF POLYAMIDE MOLDINGS Inventors: Richard Sinn,Ludwigshafen; Rolf Schellenbem Mannheim, both of Germany BadischeAnilin- & Soda-Fabrik Aktiengesellschait, Ludwigshafen/Rhein, GermanyFiled: July 14, 1971 Appl. No.: 163,406

Related US. Application Data Continuation of Ser. No. 803,299, Feb. 28,1969, abandoned.

US. Cl. 425/206, 260/78 L, 264/37, 264/331, 425/4 Int. Cl B291) 1/04,B29b 5/02, C08g 20/12 Field of Search 264/331, 216, DIG. 56, 264/37,'40;260/78 L; 23/283, 285; 425/130, 145, 4, 206, 257, 248, 217, 215

References Cited UNITED STATES PATENTS 2/1970 Heckrotte 264/3292,862,239 12/1958 Pollard et a1. 264/40 2,644,195 7/1953 Bennes et a].264/37 3,505,448 4/1970 Zijp et a]. 264/331 3,417,178 12/1968 Downing etaL. 264/331 3,454,689 7/1969 Garrison 264/331 Primary Examiner--RobertF. White Assistant Examiner-Jefi'ery R. Thurlow Attorney-Johnston, Root,O'Keeffe, Keil, Thompson & Shurtlefi [57] ABSTRACT An apparatus for theproduction of moldings by activated anionic polymerization of lactams inwhich a lactam melt containing a catalyst and a lactam melt containingan activator are separately preheated to polymerization temperature intwo melt reservoirs and supplied to a control unit including a pair ofvalves and a vertically oriented mixing chamber, mixed therein, andforced upwardly into the mold to be filled wherein valve seats for therespective valves are in the wall of said mixing chamber.

6 Claims, 4 Drawing Figures Patented Aug. 14, 1973 3,752,623

li\"1'ORS.' RICHARD 5| ROLF SCHEL BERG.

ATT'YS BY: gob zz womy waw w,

APPARATUS FOR PRODUCTION OF POLYAMIDE MOLDINGS This application is acontinuation of US. Pat. appli cation No. 803,299 filed 2/28/69, nowabandoned.

This invention relates to an apparatus for the production of polyamidemoldings by activated anionic polymerization oflactams in a mold.

It is known that activated anionic polymerization of lactams can becarried out in a mold by mixing catalyst and activator with the melt ofthe lactam to be polymerized in the mold. In this case the mixture doesnot need to be decanted and it solidifies to give the desired molding.This-method is disadvantageous especially for the production of largeand elongated moldings and for moldings having widely varyingcross-sections. It is difficult to mix the catalyst and activator withthe lactam to be polymerized under these conditions.

It is therefore preferred in most cases to introduce into the mold alactam melt which already contains the catalyst and activator. Thelactam melt containing the activator and catalyst may have already beenheated up to polymerization temperature, or the melt may have atemperature lower than the polymerization temperature and is introducedinto a mold heated to polymerization temperature.

It is also known that a lactam melt containing an acti vator and alactam melt containing a catalyst canbe heated separately topolymerization temperature and mixed by means of a mixing nozzle duringintroduction into the mold.

All these methods have disadvantages. A lactam melt containing catalystand activator can only be kept for a short time even at temperaturesbelow polymerization temperature. Such a mixture therefore has to beprocess very rapidly. However, air bubbles are readily introduced intothe mold during the molding process and these result in faults (known asbubbles) in the moldings.

It has therefore been proposed to introduce the lactam melt to bepolymerized into the mold by means of a feed tube, the lower end of thefeed tube extending into the mold beneath the surface of the lactam meltto be polymerized and if necessary being provided with deflectors toprevent too marked an eddying of the melt which has already beenintroduced into the mold. It is a disadvantage of this method thatresidues of polymerizing lactam mixture remain in the feed tube,polymerize therein and eventually clog the feed tube.

Even such pieces of apparatus do not entirely preclude the possibilityof air bubbles passing into the polymerizing melt.

. We have now found that bubble-free polyamide moldings can be preparedby activated anionic polymerization of lactams in a mold without thesaid disadvantages by heating to polymerization temperature a lactammelt containing catalyst and a lactam melt containing activatorseparately, uniting the lactam melts and allowing them to polymerize ina mold by a method in which the melt containing catalyst and the meltcontaining activator are simultaneously supplied to a mix ing zone,united therein and forced from the mixing zone upwardly into the mold tobe filled.

Apparatus for carrying out the process may therefore be as showndiagrammatically in the drawings and may comprise two reservoirs l and 2each provided with means for heating and cooling and for mixing thecontents, lines 3 and 4 capable of being heated and provided with pumps5 and 6 and leading to a control unit 11 and a mixing chamber 12separated by valves 13 and 14 from lines 3 and 4, and a mold 15 locateddirectly above the control unit 11.

In a particularly advantageous embodiment of this apparatus, theheatable lines 3 and 4 are designed as ring mains 3 and 3a and 4 and 4ain each of which a control valve 7, 8 is located.

Bubble-free rods and moldings of any cross-section and particularlymoldings having intricate shapes can be produced by activated anionicpolymerization of lactams by the said method and with the saidapparatus.

FIG. I is a diagrammatic view of the apparatus according to thisinvention. The apparatus comprises two reservoirs l and 2 provided withmeans for heating and cooling and means for mixing the contents, forexample stirred vessels capable of being heated and cooled. To each ofthe reservoirs there is connected aheatable ring main 3, 3a or 4, 40,each having a heatable pump 5 or 6 and a control valve 7 or 8. Ifnecessary, other valves may be provided in the ring mains which willpermit partial emptying of the apparatus, for example forrepairs.Commercially available pumps such as gear pumps,centrifugal pumps,diaphragm pumps or piston pumps may be used as the heatable pumps 5 and6 in the ring mains 3,3a and 4,4a.

The valves 7, 8, 9 and 10 in the ring mains 3, 3a and 4, 4a may be conevalves, ball valves, diaphragm valves or valves operated by spring orgas pressure and which automatically open when a certain pressure isreached in the line.

Complete removal of air from the system is possible by the provision ofring mains and valves so that the lactam melt can be constantly pumpedin circulation without the slightest trace of air bubbles.

Both ring mains communicate with the chamber referred to as the controlunit 11 which consists essentially of two valves 13 and 14 and a mixingchamber 12. The control unit 11 with valves 13 and I4 connects the tworing mains or loop circuits 3, 3a and 4, 4a which either allows the twocomponents to be kept separate or to be mixed. In the molding processthe components are conveyed into the mixing chamber 12 by opening valves13 and 14 and throttling or closing the control valves 7 and 8; thecomponents are mixed in the mixing chamber 12 and then forced upwardsinto the mold 15.

FIG. 2 diagrammatically illustrates on an enlarged scale a particularlyadvantageous embodiment of con trol unit 11. The control unit 11 hasonly a very small volume in relation to the mold l5.

Pneumatically controlled metal bellows valves are particularlyadvantageous as valves 13 and 14. (Hand less diaphragm valves, ballvalves or other valves may, however, also be used. In a particularembodiment these may consist of a piston sliding in a sealed cylinder.

The mixing chamber 12 is illustrated in FIGS. 3 and 3a. Thecross-sectional area of the mixing chamber at the lower end of theinverted truncated cone is about eight to 14 times that of the inflow atthe valve seats 16 and 17. It is designed at its upper edge so that themold may be placed thereon in such a way that the joint is liquid-tight.

The mixing chamber is in its upper portion, preferably shaped like aninverted truncated cone having a half apex angle of B 3 to 8 In itslower portion it continues like a breeches pipe to the valve seats 16and 17 of valves 13 and 14. The two legs of the breeches pipe taper intothe valve seats, preferably with a conicity of 3. The angle a whichgives the inclination of the legs of the breeches pipe to the centralaxis of the mixing chamber 12 may be from almost to 160, preferably from60 to 90. However, for filling molds having special shapes it may beadvantageous for the angle at which the components enter the mixingchamber to be reduced almost to 0.

The said mixing chamber 12 does not have any undercut portions, enablingthe mold 15 with the molding to be easily detached from the control unit11 after polymerization. The contents of the mixing chamber thus remainas a sprue on the polymerized casting. There is therefore a clearseparation between the unmixed (and therefore not polymerized) lactammelts downstream of the valve seats and the mixture of the two meltsupstream of the valves 13 and 14 which, after polymerization,constitutes the casting including the sprue.

The outlet openings of valves 13 and 14 are of such a size that thestreams of liquid can enter the mixing chamber 12 at a flow velocity offrom 0.1 to meters per second.

The mold 15 is located immediately above the control unit 11. Forcasting, the mold l5 and control unit 11 are connected to each other toform a liquid-tight joint. This may be done for example by means ofgravitation or by pneumatic or mechanical'pressure. Holding means whichpermit a rapid interchange of a plurality of identical or differentmolds arranged for example on a turntable are very advantageous.

It is possible to couple interchange of molds and control of valves, forexample by means of a camshaft. If means are provided on the mold 15which stop the filling process when the desired level is reached byclosing valves 13 and 14 and opening the throttled or closed controlvalves 7 and 8, the apparatus according to the invention permitssubstantially automatic production.

Lactams having at least six and particularly from six to 12 ring carbonatoms are suitable for the process according to this invention and,preferably caprolactam, enantholactam and capryllactam, and also capriclactam, laurolactam or C-substituted derivatives of lactams such as3-methylcaprolactam or 4-isopropylcaprolactam. Mixtures of these lactamsmay also be used. The said lactams may also contain minor proportions oflactams which are connected with one another by bridging members, as forexample methylene-biscaprolactan.

In addition to generally known polymerization catalysts, alkali metallactams (such as are described in German Pat. specification No.1,067,587) are particularly suitable. They are used in amounts of from0.01 to 10 percent by weight, preferably from 0.1 to 5 percent byweight, with reference to the whole weight of the polyamide-formingstarting materials. Amounts outside these ranges may, however be used,for special purposes. Mixtures of these catalysts in any proportions areof course also suitable.

Known substances such as for example N- acyllactams, isocyanates,N-cyanolactams, substituted ureas, reaction products of carbamylchlorides with heterocycles such as imidazole and the like are suitableas activators. These substances are used in amounts of from 0.05 to 10percent, preferably from 0.1 to 5 per cent, by weight with reference tothe total weight of polyamide-forming starting materials.

Additives (provided their particle size is suitable for this process)may be used in'the process according to this invention in the form ofreinforcement materials, fillers, lubricants, delustrants orstabilizers. Examples of suitable fillers are metal powder such asaluminum powder or copper powder, slate flour and diatomaceous earth.Glass fibers or other fibers are suitable as reinforcement materialsprovided they are fine enoug to permit closure of the valves.

The apparatus and process according to this invention may be operated inthe following manner:

The amount of lactam to be polymerized is advantageously divided intotwo approximately equal portions and placed in the reservoirs l and 2.They are melted and the catalyst is dissolved with thorough mixing inone portion of the melt (reservoir 1) and the activator for the anioniclactam polymerization in the other portion of the melt (reservoir 2). Itis also possible to dissolve the activator and catalyst in unequalamounts in the lactam and to regulate the mixing so that thepolymerization mixture contains the calculated parts of catalyst andactivator,

The choice of activator and catalyst depends on the shape of the moldingto be produced, on the rate of conveyance on the pumps 5 and 6 and onthe desired temperature and rate of polymerization.

Depending on the type of catalyst and activator used, theirincorporation into the separate lactam melts is carried out at from to170 C, preferably from 1 10 to 135 C.

The melt containing activator and the melt containing catalyst pass fromthe reservoirs 1 and 2 into the appropriate lines 3 and 4 or the ringmains 3, 3a and 4, 4a for example by means of gravitation or by pumppressure; The lines or ring mains are previously well deaerated. Thedeaeration of the lines may be carried out by applying subatmosphericpressure.

The lactam melts are constantly circulated by pumping and kept at thedesired polymerization temperature, which is preferably from 1 10 to 135C. Heating of the reservoirs l and 2 for the lactam melts and of thering main is adjusted to enable the lactam melts to enter the mixingchamber 12 at the said temperatures,

The amounts of the two lectams melts required to fill the mold arewithdrawn from the two lines 3 and 4 or from the two ring mains 3, 3aand 4, 4a by opening valves 13 and 14, mixed in the mixing chamber 12and forced into the mold 15 located above the same. It is advantageousat the beginning of the molding process to introduce the lactam meltsslowly into the mixing chamber 12 at first and to increase the rate ofinflow as the filling of the mold l5 proceeds. This prevents too violentan addying of the lactams melts forced through the mixing chamber 12into the mold l5 and reliably prevents inclusion of air bubbles. At thebeginning of the molding process, the pressure on the lactam melts inthe two ring mains is decreased by switching off the pumps 5 and 6 andby partially or wholly opening the control valves 7 and 8 to such anextent that the rate of flow through valves 13 and 14 is not more than0.3 meter/second, preferably only 0.2 meter/second. As soon as themixture of lactam melts in the mold 15 has reached a height of from 70to mm, the rate of flow through valves 13 and 14 may be increasedpreferably to from 0.8 to 2.0 meters/second by switching on the pumps (5and 6) and regulating the control valves 7 and 8. If necessary the flowrate may be increased to more than 4 meters/second by completely closingthe check valves. A rate of flow of about 3 meters/second isparticularly advantageous.

The time for filling the mold 15 should be such that actualpolymerization does not start until filling is completed. The viscosityof the mixed lactam melts may be from 1 to 400 centipoises upon entryinto the mold 15, but preferably from 100 to 200 centipoises.

The initiation time of the anionic lactam polymerization depends on theactivator-catalyst system used and on the mixing temperature maintained.1; may vary within the range from seconds to 10 minutes depending on thetemperature and the starting materials used and can easily be determinedby a preliminary experiment. 1n the production of fairly large castingsit is advantageous to select conditions and starting materials so thatthe filling time is not more than ,1 minute. Moldings having a weight of1 kg or less may also be cast in substantially shorter filling timeswithout any great expenditure.

The air above the level of the polymerizing lactam mixture in the mixingchamber 12 and the mold may be displaced by an indifferent gas suchasnitrogen although this is not essential when suitable activators areused. The mold itself is heated to temperatures of from 70 to 140 C,preferably from 120 to 135.:C.

The process is suitable for the production'of sections which may becircular, oval, square, rectangular or prismatic, or any other shape andparticularly for the production of moldings of intricate shape.

Moldings prepared by the process according to this invention areentirely devoid of air bubbles and streaks. Methods of carrying out theprocess according to the invention are described in greater detail inthe following Examples.

EXAMPLE 1 All the valves in the apparatus according to the invention (asshown in the drawings) are closed. Amixture of 52.79 kg of caprolactamand 210 g of sodium caprolactamate is heated to 120 C in reservoir 1 anda mixture of 54.25 kg of caprolactam and 750 g of hexamethylene-l,6-bis-(carbamoylcaprolactam) is heated to 136 C in reservoir 2. Valves9 and 10 and control valves 7 and 8 are then opened and the ring mains3, 3a and 4, 4a are filled with the respective melts by means of pumps 5and 6. The pumps 5 and 6 are switched off, the control valves 7 and 8are closed and valves 13 and 14 are opened. The lactam melts pass at aspeed of about 0.2 meter/second through the control unit 11 into acylindrical mold 15 above the same which has a diameter of 70 mm and alength of 1700 mm. When the mold has been filled to a height of about100 mm, pumps 5 and 6 are switched on again and the control valves areopened to such an extent that the rate of flow of the two melts throughvalves 13 and 14 is about. 1 meter/second. After another 15 seconds, themold has been filled to a height of 1,600 mm. Valves 13 and 14 areclosed and the control valves 7 and 8 are completely opened.

Polymerization begins 40 seconds after valves 13 and 14 have beenopened. After 1 minute, the mold is detached from the control unit 11.The finished casting may be ejected from the mold 2 minutes aftercommencement of the casting process.

A polycaprolactam rod having a smooth glossy surface is obtained whichis completely devoid of inhomogenities and bubbles. It can be machinedinto any desired engineering components or other articles. The polyamidehas a high molecular weight for it dissolves only incompletely in 96percent sulfuric acid. The content of extractable constituents is about3 percent. The modulus of elasticity of the polycaprolactam is 38,000kp/cm.

EXAMPLE 2 Reservoir 1 is charged with a mixture of 207 kg of caprolactamand 560g of sodium caprolactamate and heated to 110 C. Reservoir 2 ischarged with 217 kg of caprolactam and 3 kg of hexamethylene1,6-bis-(carbamoylcaprolactam) and heated to a temperature of 134 C. The; lactammelts are forced in the manner described in Example 1 at a flow rate ofabout 0.2 meter/second through the control unit 11 into a cylindricalmold having a diameter of 200 mm and a length of 1,700 mm. The mold isfilled to a height of about mm after about 8 seconds. The rate of flowof the 2 melts through valves 13 and 14 is then increased to about 1meter/second and finally, after another 8 seconds, when the mold hasbeen filled to a height of about 480 mm, to abput 3 meters/second. Themold is almost full after another 8 seconds. Valves 13 and 14 are closedand the control valves completely opened.

Two minutes after the beginning of the molding process, the mold [isremoved from the control unit 11. The finished castinlg may be ejectedfrom the mold after only 1 minute.

The casting is free from bubbles and completely homogeneous. Thepolyamide is only incompletely soluble in concentrated sulfuric acid andcontains about 3 percent of constituents capable of being extracted withmethanol.

EXAMPLE 3 A mold for the production of a marine propeller is placed onthe control unit 11 of the apparatus according to this invention.

A melt of 103 kg of caprolactam and 280 g of sodium caprolactamate,heated to C, is contained in reservoir 1. A melt, heated to 122 C, of107 kg of caprolactam and 1.2 kg ofhexamethylene-l,o-bis-(carbamoylcaprolactam) is contained in reservoir2. The lactam melts are introduced into the mold in the manner describedin Example 1, first at a rate of about 0.3 meter/- second and later at arate of about 3 meters/second. The mold is completely filled after about20 seconds.

Two minutes after the commencement of casting, the mold may be removedfrom the control unit 11. The marine propeller may be ejected afteranother 3 minutes.

A bubble-free marine propeller is obtained which has a modulus ofelasticity of about 35,000 kp/cm and weighs about 40 kg.

We claim:

1. Apparatus for carrying out the process for the production of moldingsby activated anionic polymerization of lactams having at least six ringcarbons, in which a lactam melt containing a catalyst and a lactam meltcontaining an activator are separately heated to polymerizationtemperature and allowed to polymerize, in a mold, which comprises twomelt reservoirs, means associated with each reservoir for heating orcooling the melt therein, melt-agitating means in each reservoir, acontrol unit including a pair of valves and a vertically oriented mixingchamber, respective pipelines communicating said mixing chamber andrespective reservoirs via respective valves in said control unit, valveseats for the respective valves in the wall of said mixing chamber,pumps in respective pipelines, a melt discharge opening in the upperface of said mixing chamber, a vertically oriented mold detachablymounted on said upper face directly above said chamber and incommunication with said discharge opening, in which mold the unitedmelts polymerize as a casting, and the walls of said 'mixing chamberbeing free from undercut portions, whereby the mold and the polymerizedcasting therein may be detached from control unit after polymerizationwith the contents of the mixing chamber simultaneously being removed asa polymerized sprue on said casting.

2. Apparatus as claimed in claim 1 wherein said mixing chamber has theshape of an invertedjtruncated cone.

3. Apparatus as claimed in claim 1, pipe means for circulating therespective pumped melts through respective loop circuits back to therespective reservoirs, and throttle valve means in said loop circuitsfor throt' tling or closing said loop circuits when said pair of valvesare open.

4. Apparatus for carrying out the process for the production of moldingsby activated anionic polymerization of lactams having at least six ringcarboings, in which a lactam melt containing a catalyst and a lactammelt containing an activator are separately heated to polymerizationtemperature and allowed to polymerize in a mold, which comprises twomelt reservoirs, means associated with each reservoir for heating orcooling the melt therein, melt-agitating means in each reservoir, acontrol unit including a pair of valves and a vertically oriented mixingchamber, said mixing chamber having the shape of an inverted, truncatedcone, respective pipelines communicating said mixing chamber andrespective reservoirs via respective valves in said control unit, valveseats for the respective valves in the lower portion of said mixingchamber, pumps in respective pipelines, a melt discharge opening in theupper face of said mixing chamber, a vertically oriented mold detachablymounted on said upper face directly above said chamber and incommunication with said discharge opening, in which mold the unitedmelts polymerize as a casting, and the walls of said mixing chamberbeing free from undercut portions, whereby the mold and the polymerizedcasting therein may be detached from control unit after polymerizationwith the contents of the mixing chamber simultaneously being removed asa olymerized sprue on said casting.

5. Apparat s as claimed in claim 4, the crosssectional area of the lowerend of said inverted, truncated cone mixing chamber being eight to 14times the inflow area of said valve seats.

6. Apparatus as claimed in claim 4, the wall of said inverted, truncatedcone mixing chamber tapering at a half-apex angle of 3 to 8.

32 3 UNITED STATES PATENT oFTTcE CERTIFICATE OF CORRECTION Patent No.5,752,625 Dated August 14, 1975 Inventor) Richard Sinn and RolfSchellenberg It is oerti'fied that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

First page, left-hand column, ninth line "July 14, 1971" should readJuly 16?, 1971 First page, left-handoolumn, eleventh line, insert [50]Foreign Application Priorit Data a March 2,1968; Germany P 17 20 552.0Column line 1H1, "loctams" should read laiotams Signedandt sealed this27th day of November 1973.

SEAL Attest:

EDWARD M.PLETCHER,JR. RENE D. Attesting Office-r Acting Commissioner ofPatents

2. Apparatus as claimed in claim 1 wherein said mixing chamber has theshape of an inverted, truncated cone.
 3. Apparatus as claimed in claim1, pipe means for circulating the respective pumped melts throughrespective loop circuits back to the respective reservoirs, and throttlevalve means in said loop circuits for throttling or closing said loopcircuits when said pair of valves are open.
 4. Apparatus for carryingout the process for the production of moldings by activated anionicpolymerization of lactams having at least six ring carbons, in which alactam melt containing a catalyst and a lactam melt containing anactivator are separately heated to polymerization temperature andallowed to polymerize in a mold, which comprises two melt reservoirs,means associated with each reservoir for heating or cooling the melttherein, melt-agitaTing means in each reservoir, a control unitincluding a pair of valves and a vertically oriented mixing chamber,said mixing chamber having the shape of an inverted, truncated cone,respective pipelines communicating said mixing chamber and respectivereservoirs via respective valves in said control unit, valve seats forthe respective valves in the lower portion of said mixing chamber, pumpsin respective pipelines, a melt discharge opening in the upper face ofsaid mixing chamber, a vertically oriented mold detachably mounted onsaid upper face directly above said chamber and in communication withsaid discharge opening, in which mold the united melts polymerize as acasting, and the walls of said mixing chamber being free from undercutportions, whereby the mold and the polymerized casting therein may bedetached from control unit after polymerization with the contents of themixing chamber simultaneously being removed as a polymerized sprue onsaid casting.
 5. Apparatus as claimed in claim 4, the cross-sectionalarea of the lower end of said inverted, truncated cone mixing chamberbeing eight to 14 times the inflow area of said valve seats. 6.Apparatus as claimed in claim 4, the wall of said inverted, truncatedcone mixing chamber tapering at a half-apex angle of 3* to 8*.